Whole blood comprises cellular components, namely red blood cells (erythrocytes), white blood cells (leukocytes) and platelets (thrombocytes), which are suspended in a liquid component, plasma, consisting of water and solutes (in particular proteins, electrolytes and metabolites). The white blood cells comprise mononuclear cells (lymphocytes, monocytes, stem cells) and polymorphonuclear cells (granulocytes, comprising neutrophils, eosinophils and basophils).
Each kind of blood cell performs a specific function: red blood cells transport oxygen from the lungs to body cells and carbon dioxide from body cells to the lungs; white blood cells are part of the immune system, which protects the body against microorganisms and foreign matter; platelets help prevent blood loss by forming a plug at the site of vascular injuries.
Plasma proteins also perform specific functions: clotting proteins (coagulation factors) assist in clot formation by holding the platelet plug in place, globulins (antibodies) neutralize foreign substances as part of the immune response, and albumin helps maintain the water content and the viscosity of the plasma, both of which are necessary to keep a normal blood pressure.
Because of the specificity of the functions fulfilled by the blood cells and by the plasma proteins, it is customary today to infuse or inject into a patient only the blood component or the fraction thereof (e.g. coagulation factors) needed by the patient to address a particular surgical or medical condition. Whole blood may still be infused to replace blood lost during trauma or surgery, however, most of the time, only the blood component missing or destroyed by disease or chemotherapy is administered.
The whole blood or blood components or any fraction thereof that are infused or injected into patients originate from healthy donors (who can be the future recipients of the blood product, in case of an autologous donation). A blood donation generally consists of either about 450 ml (one pint) or about 500 ml of whole blood.
In accordance with the current infusion practices mentioned above, donated whole blood is usually separated into two or three blood components, namely plasma and red blood cells, or plasma, red blood cells and platelets.
The separation of whole blood into two blood products includes a centrifugation phase, by which blood is separated into plasma and packed red blood cells, and an optional filtration phase, by which platelets and white blood cells are removed from the packed red blood cells.
The separation of whole blood into three blood products includes a centrifugation phase, by which blood is separated into a first component mainly comprising plasma, a second component mainly comprising platelets and a third component mainly comprising red blood cells. In a further filtration stage, which is optional, white blood cells are removed from the packed red blood cells. Platelets separated from four to six blood donations are pooled to form a transfusion dose and white blood cells are removed therefrom by filtration.
It is important to remove white blood cells from whole blood and blood components (platelets, packed red blood cells) for the following reasons, in particular: during storage, white blood cells release cytokines, which, when transfused into a patient can cause febrile non-hemolytic transfusion reactions. Also, after multiple transfusions, some patient develop antibodies to human leukocytes antigens (HLA) that react to HLA on the membrane of donor white cells. HLA antibodies also can cause transfusion reactions in patients who receive multiple transfusions. White blood cells are also responsible for the transmission of diseases.
International patent application WO 2004/018021 describes a method and an apparatus for separating a volume of whole blood into either a plasma component and a red blood cell component; or a plasma component, a red blood cell component and a platelet component.
The apparatus comprises a centrifuge adapted to cooperate with an annular separation bag for whole blood, which is connected to either a plasma component bag and a red blood cell component bag or a plasma component bag, a red blood cell component bag and a platelet component bag.
The centrifuge includes: a rotor for spinning the separation bag and centrifuging the whole blood contained therein, the rotor having a turntable for supporting the separation bag and a central compartment for containing the component bags connected to the separation bag; and a squeezing system for squeezing the separation bag and causing the transfer of the plasma component from the separation bag into the plasma component bag, of the red blood cell component into the red blood cell component bag and, as the case may be, of the platelet component into the platelet component bag.
According to the method described in International patent application WO 2004/018021, the removal of white blood cells (so-called “leukoreduction”) from the various blood components can be performed either before centrifugation of the whole blood or after separation of the whole blood into two or three components. In the pre-centrifugation removal process, the white blood cells (and, as the case may be platelets) are removed by filtration from the whole blood during the transfer thereof from a collection bag into the separation bag. In the post-separation process, white blood cells, (and as the case may be platelets), are removed by filtration from the red blood cell component during the transfer thereof from a transfer bag into a red blood cell product bag.